In microscopy, structured illumination is used for depth discrimination in the wide field [1]1 and for enhancing the resolution and the contrast [2]. Generally, a grating or another periodic structure is projected into the specimen [3] or an interference pattern is generated in the specimen by means of interference of coherent component beams [4]. Subsequently, images that differ from one another due to the shift of the illumination structure are suitably blended with one another so as to obtain an optical sectional image or an image with enhanced contrast and enhanced resolution [5,6]. 1 Bracketed references refer to the list of references at the end of the specification prior to the claims.
All of these methods have in common that different phase angles of the periodic structure are projected into the specimen; at the same time, it is desirable that the phase angle can be controlled as accurately as possible and that a rapid change between various settings of the phase angle can be made. An inaccurate shift of the projected structure can lead to artifacts (e.g., striation) in the image. The accuracy, speed, reproducibility and calibratability of the setting of the phase angle are therefore very important characteristics for implementing such a method for structured illumination.
In addition, in some approaches to the implementation of the method of the structured illumination, in particular in the high-resolution approach [7], a rotation of the orientation of the projected structure is required.